Method of producing dies for extruding externally finned tubes



5. 1949. A. w. HALLBERG METHOD OF PRODUCING DIES FOR EXTRUDING EXTERNALLY-FINNED TUBES 2 Sheets-Sheet 1 Filed Nov 29, 1946 km W 17 e y Z w a r! .M M M w W w/ Q l hl 7 Q Feb. 15, 1-949. A, 'w. HALLBERG 2,461,640

METHOD OF PRODUCING DIES FOR EXTR-UDING EXTERNALLY-FINNED TUBES Filed Nov. 29, 1946 2 SheetsSheet 2 the prior art.

Patented Feb. 15, 1949 METHOD OF PRODUCING DIES FOR EX- TRUDING EXTERNALLY FINNED TUBES August W. Hallberg, Waterbury, Conn, assignor toCha se Brass & Copper Co. Incorporated,

Waterbury, Coma, a corporation Application November 29, 1948, Serial No. 713,160

2 Claims. (01. 76-107) The present invention relates to improvements in extrusion-dies and relates more particularly 'to. extrusion-dies for producing tubes having integral longitudinally-extending fins upon their outer peripheries. Such finned tubes are primarily useful as heat-exchange tubes but are avaiiableior a wide variety of other uses.

For heat-exchange purposes. a finned tube of the character referred to is most effective if it is provided with a relatively-large number of slender or thin fins rather than being provided with a lesser number of thicker fins. Heat-exchange tubes of the character first referred to. provide a much larger surface area for the-transfer of heat and the advantages thereof are well recognized in the art.

.Prior to the present invention. however, it has .not beeneconomically feasible to provide by extrusion methods the desired characteristics, especially on tubes of small diameters, since 'suitable extrusion-dies have been difncult and expensive to produce by conventional methods employing fragile broaches having thin or slender broaching-ribs thereon.

It is one of the mainobjects of the present invention, therefore, to provide a superior die for extruding externally-finned tubes and which may be produced at a low cost for manufacture.

Another object of the present invention .is to provide a superior die of the character referred to which is both accurate and durable in use.

with the above and other objects in view, as

will appear to those skilled in the art from the,

present disclosure, this invention includes all features in the said disclosure which are novel over In the accompanying drawings, in which certain modes of carrying out the present invention are shown for illustrative purposes:

Fig. 1 is a view of 'a partially-completed diebody suitable for carrying out the present invention andlooking toward theinner or upper end thereof; f

Fig. 2 is a transverse sectional view taken on v the line 2-2 of Fig. l;

I Fig. 3 is a view similar to Fig. 1 but on alarger scale and showing the die-body after the same has been provided with an annular series of bladereceiving grooves; v

Fig. 4 is a view partly in side elevation and partly in transverse-section taken on the line 4-4 of Fig. 3:

Fig. 5 is a perspective view of one of the multiplicity of. blades .suitable for insertion into the blade receiving grooves shown in Figs. 3 and no. 8 isasectional view similar to Fig. 4, but

'ture mounted in the lower end of an extrusion-- showing a gauge-plug inserted into the clearancepassage of the die-body and a plurality of blades respectively installed in the blade-receiving grooves of the die-body; 1

Fig. 7 is a broken view similar to Fig. 3, but

showing the blades in place, as in Fig. 6;

. Fig. 8 is a view similar to Figs. 3 and 7, but showing the structure after the projecting-ends of the blades have been trimmed oil and a retaining-ring has been mounted around the blademounting neck of the die-body to back up and retain the blades against radial outward movement;

Fig. 9 is a central-longitudinal sectional view through the completed die-structure, taken on the line 99 of Fig. 8, but showing the said struccylinder, together with a mandrel which is extended into the extrusion-passage of the diestructure preparatory to extruding a longitudinally-finned tube of the character shown in Fig. 10; and

Fig. 10 is a perspective view of a portion of a longitudinally-finned tube which, may be produced by means of the structure of the preceding figures.

For a better understanding of atpreferred mode of carrying out the present invention, reference may first be had to Figs. 8 and 9 wherein a com-. pleted extrusion-die is shown, and to Fig. 10 which illustrates an externally-finned tube which may be produced by means of the present invention.

The completed extrusion-die chosen for illustration in the figures just referred to, includes a die-body generally designated by the reference character l0 and which is preferably formed of high-grade steel or other equivalent material.

The said die-body is generally of cylindrical form and is provided upon its outer periphery with threads II. The said die-body is formed at its inner or upper end with an integral axiallyextending blade-mounting neck l2 preferably having a smooth outer periphery. The said neck Y is formed axially with an extrusion-passage l3 which has a diameter substantially corresponding to the external diameter of the body-portion i4 of an extemally-finned tube generally designated by the reference character I! and shown in Fig.

Ill. The said externally-finned tube'li also in- "cludes a plurality of substantially-longitudinal is formed with a clearance-passage l1 which is coaxial with the extrusion-passage l3 and com-- municates at its inner end therewith. {Ihe diameter of the clearance passage i1 is prefer-'- ably such as to substantially correspond to the since the said neck has a lesser diameter than the remainder of the die-body.

Formed in the blade-mounting neck l2 of the die-body Ills a'multiplicity of blade-receiving grooves l9 all radiating, in the instance shown, from the central-longitudinal axis of the diebody It and equidistantly spaced from each other in a circumferential direction. At their inner i ends, each of the grooves l 9 intersects the extrusion-passage II, as well as a portion of the clearance-passage ll. At their outer ends, each of the blade-receiving grooves l'9 intersects the outer periphery of the blade-mounting neck l2.

The blade-receiving grooves l9 above referred to preferably have a depth, in a direction axially of the structure, corresponding to the length or height of the blade-mounting neck l2 so that the lower edges of the said grooves coincide with the surface of the shoulder II at the base of the said neck l2.

Respectively mounted with a. tight'driveor shrink-lit in the blade-receiving grooves I 9 of the blade-mounting neck l2, are a plurality of hardened steel plate-like blades which are of substantially-rectangular form in the instance shown, as will be apparent by reference to Fig. 5 in particular.

The radially-inner edges of each of the blades 20 preferably coincide with the surface of the clearance-passage." in the die-body to thus leave the radially-inner portions of the grooves l9 vacant, to provide fin-forming passages 2| for the formation of the fins f6.

' The respectively-radially-outer edges of the blades 20 preferably coincide with the outer periphery of the blade-mounting neck l2, and each of the said blades has a width in the direction of the axis of the structure such as to cor-.

respond to the length of the blade-mounting neck 12.

Applied with a forceor shrink-fit over the outer periphery of the blade-mounting neck I2, is a steelor other suitable retaining-ring 22 having a width in an axial direction corresponding to the height of the said blade-mounting neck. The inner periphery of the said retainingring" provides a seat against which the radiallyouter edges of each of the multiplicity of blades 22 engage. to thus be held against radially-outward displacement.

In its lower face, opposite the blade-mounting neck 12, the die-body l0 ispreferably formed with a pair of diametrically-opposite wrenchreceivlng sockets 23-adapted to receive a spannerwrench or other suitable tool by means of which the die-structure may be threaded into and unthreaded from an internally-threaded cavity 2 formed in the lower portion of an extrusioncylinder 25. The upper portion of the cavity 24 is untreaded and is of a lesser diameter than the diameter of the main portion of the die-body l0.

when tightly threaded intothe cavity 24, the die-structure serves to seat the upper edges of itsblades 20 and its retaining-ring- 22 against cavity, all as is shown in Fig. 9.

In a manner well known in the art, the extrusion-cylinder 25 may be formed with a billetchamber 21 having a constricted outlet-passage 28 at its lower end. Preferably the said outletpassage is of a diameter corresponding or substantially corresponding to the extreme outer diameter of the externally-finned tube II measured to the extremity of its fins l6. Thus, under the arrangement just referred to, the wall of the outlet-passage 28 coincides with the radiallyinner edges of the blades 20 and with the wall of the clearance-passage ll in the die-body I'll.

A mandrel 29 may be extended downwardly through the billet-chamber 2'I so that its lower or outer end extends into and is centralized within the extrusion-passage ll of the die-body ID, in a manner shown in Fig. 9. The diameter of the mandrel 2! is such as to provide the desired internal diameter of the body-portion ll of the tube l5 of Fig. 10. The externally-finned tube It may have an'internal diameter, for instance, of about 1%, an over-all external diameter of about /4" and a wall thickness ofthe body-portion ll of about is".

Now, when a thick-walled tubular billet of copper or the like (not shown) is placed in the billet-chamber 21 of the extrusion-cylinder 25 with the mandrel 29 extending through its hollow interior, a suitable impact-ram may be utilized to force the said billet through the extrusionpassage 13 of the die-body ill to thus produce the temperatures.

-tilting displacement will occur.

rials, lesser heats may be employed or the material, where suitable, may be extruded at room The extrusion forces, of course, exert great strains upon the die-structure, but due to the fact that the blades 20 are clamped between the up- I per wall 26 of the cavity 24 in the extrusioncylinder 25 and the bottoms of the blade-receiving grooves ID in the die-body iii, no vertical or Radial displacement will not occur due to the fact that the radially-outer edges of each of the blades 20 are backed up by the inner periphery of the retainlug-ring 22. i

In producing the die-structure above described, it is preferred to first prepare a partially-formed die-body of the character illustrated in" Figs. 1 and 2. wherein the die-body is complete'save for the formation therein of the "blade-receiving grooves l9 and the installation in the said grooves of the plurality of blades 20.

A thin circular saw may now be passed diametrically across the blade-mounting neck i2 while rotating in a plane substantially parallel with the axis of the said neck to form the equallyspaced blade-receiving grooves l9. In the instance shown, each blade-receiving groove I9 has a similar groove located diametrically opposite and under such circumstances, a straight" diametrical pass of a saw or its equivalent will, produce two grooves at one setting. After producing a pair of diametrically-opposite grooves, the partially-completed die-body may be indexed around and subsequent pairs of grooves I! produced until the annular series is completed.

A gauge-plug, such as 30 shown in Fig. 6, may be introduced into the clearance-passage ll of the die-body I 0 so as to overlap and close a portion of the radially-inner end of each of the bladereceiving grooves IS. The required number of plate-like blades 20 may be now respectively intheir-radially-inner edges abut against the gaugeplug' 30 and their respective loweredges firmly seated against the bottoms of their complemental grooves 19. Preferably and as shown, the bladesare of such length in a radial direction as to project slightly beyond the outer periphery of the blade-mounting neck I 2, in the manner illustrated inFigs.6and7.- Y

The mounting of the blades 20 in their respective blade-receiving grooves I! may be accomplished in a wide variety of manners such, for instance, as by a force-fit and preferably after the said blades have been hardened and tempered. The blades 20 may also be inserted into the blade-receiving grooves. l9 by heating the diebody 10 to a degree sufllcient to cause a slight widening of its blade-receiving grooves l9, whereupon the blades 20, in a relatively-cooler condition, may be inserted so that when the said diebody cools, the said blades will be firmly gripped in place.

The structure, in substantially the condition shown in Figs. 6 and 7, may now be mounted in a suitable grinding fixture and the projecting outer ends of the blades may be ground to flushness with the periphery of the blade-receiving neck l2 which latter also may be coincidentally ground toaccuratesize.

' The retaining-ring 22 may now be installed over the blade-mounting neck I! of the die-body I. by first heating the said ring to expand it relative to the said neck and then applying it in place and permitting it to shrink into tight engagement not only with the periphery of the said neck but withthe radially-outer ends of the said blades. If desired, a force-fit may be substituted for the shrink-fit referred to.

The upper surface of the structure now in substantially the condition illustrated in Figs. 8 and 9 may be ground so as to insure the flushness of the upper surface of the neck II, the upper surfaces of the blades 20 and the upper surface of the retaining-ring 22.

The completed die-structure may now be inserted into the cavity 24 in the extrusion-cylinder 2i and utilized in the manner before described to produce externally-flnnedtubes II, such as is shown in Fig. 10.

The radially-inner edges of the series of blades 20 provide the surface against which the respec-.

tive outer edges of the ribs l8 of the tube It will be formed and gauged. Thus, in eflect, the finforming passages 2| are bounded by the side walls of the radially-inner portions of the blade-receiv- 8 grooves 18 and the radially-inner edges of the blades Ill.

Extrusion-dies for producing other than the round-externally-flnned tubes illustrated, may also be produced in accordance with the present invention.

In the manner above described, very slender fin-forming passages such as 2| may be provided 'withoutrequiring the use of delicate broaches or the like;

The invention may be carried out in other speciflc ways than those herein set forth without departing from the spiritv and essential characteristics of the invention, and the present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all chan' es coming within the meaning and equivalency' ange of the appended claims are intendedto be embraced therein.

I claim:

1. The method of producing dies for extruding externally-finned tubes, which method includes the steps of providing a die-body, forming a longi- 5 tudinal extruding-passage axially therethrough, forming a clearance-passage in said die-body for the fins of the tube to be extruded by boring I a concentric counterbore in the lower end'of said extruding-passage, forming a plurality of blade- 10 receiving grooves in said die-body by cutting a plurality of transverse grooves across the upper end thereof to intersect both the inner sides of said extruding-passage and the inner sides of said clearance-passage, said transverse grooves lying in planes which are coextensive with and intersect the longitudinal axis of said die-body, mounting plate-like blades in each of said transverse grooves, inserting a plug-gauge into said counterbore into engagement with the lower ends of said plate-like blades to locate the inner edges of said blades radially outwardly with respect to the inner surface of said extruding-passage and substantially flush with the inner surface of said clearance-passage and then clamping a ring around the upper end of said die-body to provide seats for the outer edges of said plate-like blades. 2. The method of producing dies for extruding externally-finned tubes, which method includes the steps of providing a die-body, forming a neckportion of reduced transverse dimensions on the upper end thereof, forming a longitudinal extrading-passage extending axially through said die-body and through the neck-portion thereof, forming a clearance-passage in said die-body for the fins of the tube to be extruded by boring a concentric counterbore in the lower end of said extruding-passage, said counterbore terminating within said extruding-passage in a plane above the juncture of said neck-portion with the body 40 of said die, forming a plurality of blade-receiving grooves in said neck-portion by cutting a plurality of transverse grooves thereacross so that the bottom edges of' said grooves are flush with the juncture of said neck-portion and the body of said die, said transverse grooves also intersecting both the inner sides of said extrudingpassage and the inner sides of the upper endportion of said clearance-passage and lying in planes which are coextensive with and intersect the longitudinal axis of said die-body, mounting plate-like blades in each of said transverse grooves, inserting a plug-gauge up into said counterbore to a position above the bottom edges of said grooves and into engagement with the inner edges of said blades radially outwardly with respect to the inner surface of said extrudingpassage and substantially flush with the inner surface of the upper end-portion of said clearance-passage and then clamping a ring around the neck-portion of said die-body to provide seats for the outer edges of said plate-like blades.

' AUGUST W. HALL-BERG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS lower ends of said plate-like blades to locate the 

